A study of twenty solar farms in southern France found that soil biodiversity and respiration significantly decrease under panels, especially in mowed areas, while plant traits such as height and leaf area can increase under grazing. The researchers emphasized that climate, type of management and sun protection all determine the responses of the soil and plants.
A French research team has analyzed the impact of solar farms on the mesofauna, respiration and plant properties of the soil by collecting samples from twenty different parks in southern France.
“This study has several new aspects,” said corresponding author Arnaud Lec’hvien pv magazine. “Firstly, the study was carried out in two regions with different climatic conditions, examining a large number of sites in each region. Secondly, we compared two management methods: mowing and grazing. Thirdly, many new variables were studied, in particular the functional properties of plants and the soil food web.”
Lec’hvien added that the results show a decrease in biodiversity under the solar panels. “But,” he added, “the most surprising finding is that the soil food web is significantly more affected by mown than by grazed areas. Conversely, the opposite was observed for pollinators.”
The research focused on functional properties, physicochemical properties of the soil, small communities of soil animals and soil respiration.
It was carried out in two southern French regions – the Atlantic Ocean and the Mediterranean Sea – which differ in climate, soil types and vegetation. Ten solar parks have been selected per region: five managed by mowing and five by grazing. Three positions were examined within each park: under solar panels, between panel rows and an unshaded spot. Each treatment was repeated in four blocks per park.
Measurements in the Mediterranean Sea were carried out in May 2023 and in the Atlantic Ocean in June 2023. Some analyzes were carried out on site, while other samples were transported to the laboratory. Each sample consisted of a composite soil sample, 6 cm deep, from the same position type within a park. The team measured plant properties; soil properties, including temperature, moisture and nutrient content; soil fauna such as mites and springtails; and soil respiration as an indicator of biological activity.
The results showed that species richness under panels was 37.5% lower compared to areas without shade, while chlorophyll content increased by approximately 12%. In grazed parks, plant height under panels increased by up to 72% and specific leaf area was up to 46% higher. Soil temperatures were 2–4.5 °C lower under panels, and soil moisture was reduced by up to 42% in the Mediterranean.
The soil fauna was strongly influenced by solar panels. Springtail abundance decreased among panels by 74–76%, and total mesofauna decreased by approximately 38%. Non-predatory mites decreased by approximately 45-65% at Atlantic sites, while predatory mites showed no significant change.
Meanwhile, soil respiration, a measure of biological activity, was found to decline by around 62% overall, with declines of more than 50% in the Mediterranean and 55-58% in mowed Atlantic parks. Grazed Atlantic sites showed no significant effect.
“Future research will investigate how the climatic gradient in each region influences the impact of solar panels by comparing it to open grassland,” said Lec’hvien. “This work will investigate interactions between plants and soil, as well as trophic interactions between soil fauna, including macro- and mesofauna.”
The research work is described in “Effects of solar panels and management on soil mesofauna, respiration and plant properties in solar farms of two southern French regions”, published in the Journal of Environmental Management. Scientists from the French University of Aix Marseille, the University of Avignon, the University of Montpellier, University of Tours and the French energy company Engie participated in the study.
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